This invention relates generally to sound radiators for mounting in a suspended ceiling grid, and more specifically to sound radiators that are fire rated while at the same time retaining the ability to reproduce high fidelity sound.
Flat panel sound radiators have improved significantly in their ability to reproduce high fidelity sound for use in background music and paging systems. Such radiators are particularly suited to and have increasingly been employed in commercial sound distribution systems. In such systems, flat panel radiators are mounted within the grid work of suspended ceilings facing downwardly into a space to project sound into the space. The rear or back portion of the radiator is thus located in the plenum space; that is, the space above the plane of the suspended ceiling. In many cases, these flat panel sound radiators are virtually indistinguishable in appearance from standard ceiling tiles that surround the radiators, yet are able to reproduce sound with astonishing fidelity. Since the sound is reproduced primarily through distributed mode reproduction in the panel, it is perceived by those in the space as being uniform and pleasing throughout the space.
One high fidelity flat panel sound radiator is disclosed and claimed in U.S. Pat. No. 6,386,315 of Roy et al., which is assigned to the assignee of the present invention and is hereby incorporated by reference. The sound radiator disclosed in this patent includes a metal frame sized to fit within an opening of a suspended ceiling grid. A radiator panel or diaphragm is mounted within the frame and is supported by resilient foam isolators, which facilitate vibration of the panel to produce sound while isolating the vibration from the surrounding ceiling grid. A rigid metal bridge is mounted at its ends to opposite sides of the metal frame and spans the frame just above the diaphragm. The bridge houses the various electronic components and connectors of the system and may also support one or more magnetic transducers that are operably coupled to the diaphragm. The transducers convert electrical signals corresponding to an audio program into corresponding vibrational motion, which is imparted to the diaphragm for reproducing the audio program. The bridge mounted transducer arrangement has been found to enhance the fidelity of such flat panel radiators because, among other reasons, the weight of the transducer is supported by the bridge, allowing for a more massive magnet structure, and allowing the diaphragm to float freely within the frame. Other similar flat panel radiator designs are disclosed in pending U.S. patent application Ser. No. 10/003,929 entitled Flat Panel Sound Radiator with Supported Exciter and Compliant Surround, and U.S. patent application Ser. No. 10/003,928 entitled Flat Panel Sound Radiator with Enhanced Audio Performance, each of which is owned by the assignee of the present invention and is hereby incorporated by reference.
While flat panel sound radiators for suspended ceiling installation have indeed improved significantly and are becoming more ubiquitous in commercial spaces, they nevertheless have encountered some obstacles. For example, some of the materials typically used in the manufacture of flat panel sound radiators to achieve high fidelity sound, such as craft paper and plastic diaphragms and foam isolators, are not inherently resistant to fire hazards such as heat, smoke, flames, and flaming debris in the event of a fire in the plenum space. This can be a serious problem where building codes require that all products mounted in the plenum space above a suspended ceiling be fire rated. In fact, some flat panel radiators have not been able to pass the Underwriters Laboratory (UL) standard fire test UL 2043, which, in effect, renders them unusable because they cannot be classified as being xe2x80x9cfire rated.xe2x80x9d The term xe2x80x9cfire ratedxe2x80x9d as used herein means conforming to the requirements of specified fire test methods, such as the above mentioned UL 2043 fire test for heat and visible smoke release for discrete products and their accessories installed in air handling spaces.
One possible method of improving the fire performance of a flat panel radiator assembly is to enclose the back of the assembly with a metal box, thereby isolating the diaphragm and other susceptible components from any fire hazard within the plenum space. Unfortunately, this also has the effect of seriously degrading the fidelity of audio material reproduced by the radiator assembly because, among other things, the trapped air within the box acts to dampen vibrations of the diaphragm and because sonic resonances and reflections form in the box, which are then transmitted through the diaphragm into a space below. Another possible solution to the problem might be to manufacture the various components of the system, i.e. the diaphragm and foam isolators, from materials that have improved fire properties. Unfortunately, this might not be a practical solution because materials with good or improved fire properties may not be conducive to the production of high fidelity sound.
Accordingly, a need exists for a high fidelity flat panel sound radiator system for use in suspended ceiling environments that also provides superior fire performance to meet even the most stringent fire tests and building codes. Such a system should produce sound that is virtually indistinguishable in fidelity from sound produced by current high fidelity flat panel radiators while simultaneously protecting susceptible components of the system from fire, heat, smoke, and burning debris. It is to the provision of such a high fidelity flat panel sound radiator system that the present invention is primarily directed, although the concept is equally applicable to any other type of sound radiator such as a traditional cone or piston-type loudspeaker.
Briefly described, the present invention, in a preferred embodiment thereof, comprises a flat panel sound radiator assembly that meets plenum fire rating codes and yet that reproduces high fidelity sound for background music, paging, and other audio applications. In the preferred embodiment, the radiator comprises a rectangular metal frame that supports a diaphragm designed to reproduce audio material. The diaphragm is supported in the frame by a compliant isolator, which may take the form of a foam surround. The compliant isolator enhances the fidelity of sound reproduced by the diaphragm and isolates the diaphragm from the frame and the surrounding ceiling grid structures. An elongated bridge is attached at its ends to opposite legs of the metal frame and spans the flat panel radiator just above the back surface of the diaphragm. The bridge supports various electronic components of the radiator such as a volume control, a transformer, and connecting wires. The bridge may also support one or more magnetic transducers that are operatively coupled to the diaphragm for imparting to the diaphragm vibrations corresponding to an audio program to be reproduced.
A back box assembly is mounted to the frame and to the bridge and is configured to enclose the entire back of the sound radiator. In the preferred embodiment, the back box is formed from a pair of generally rectangular shells, each of which is attached to the radiator on a corresponding side of the bridge. The back box thus encloses and isolates the diaphragm, foam surround, and other fire susceptible components of the radiator assembly from the surrounding environment within a plenum space. In the event of a fire in the plenum, these elements are protected by the back box assembly from heat, flame, smoke, and flaming debris and, accordingly, the flat panel radiator of this invention is fire rated and easily meets or exceeds plenum fire protective codes and passes the standard UL 2043 fire protection test.
In order to provide such fire performance without adversely affecting the fidelity of sound reproduced by the diaphragm of the radiator, the upper panels of the back box shells are partially cut out and one or more panels of a porous material such as a non-woven fiberglass or other appropriate material is mounted in the cut-out. The porous material provides adequate protection from heat and flames, but, because of its porous nature, air is permitted to flow relatively freely through the material. As a result, the diaphragm is free to vibrate when reproducing an audio program without being damped by a compliant volume of air trapped behind the diaphragm as would be the case in a closed back box. Sound degrading resonances and reflections also are eliminated. Accordingly, the flat panel radiator of this invention reproduces an audio program with fidelity that is equal to or just slightly, but acceptably, degraded from a sound radiator with no fire rated back box at all.
This invention thus provides a fire rated flat panel sound radiator for installation in a suspended ceiling that retains the high fidelity sound reproduction characteristics of flat panel radiators such as those disclosed in the incorporated references. Radiators constructed according to the invention easily pass UL fire tests and can be installed in commercial buildings with stringent plenum fire rating requirements. This invention is equally applicable to any loudspeaker such as a traditional cone or piston device when similarly applied within a suspended ceiling system.
These and other features, objects, and advantages of the invention will become more apparent upon review of the detailed description set forth below taken in conjunction with the accompanying drawing figures, which are briefly described as follows.